The present invention relates in general to a method for setting parameters required for blasting utilizing bar-like charge, more specifically to a method for setting parameters required for blasting with a bar-like charge system having a drilled blast hole diameter d, which is indispensable to the bar-like charge, associated mutually with other parameters such as a blast hole length M, a filler length P, a charge length N=M-P, charge specific gravity A, a fracture rock volume V, a blasting coefficient c, etc., employing basic equations capable of being applied to blasting for one and two free surface(s), as well as to blasting with a blast hole angle of .alpha.=90.degree., and .alpha.&lt;90.degree..
Chemical explosives capable of causing explosions associated with heating and burning were invented in China in ancient times in the era Tang (618-907). Alfred Novel developed "Dynamite" made primarily of nitroglycerine, in the spring of 1864, obtained a Swedish patent. Since then, it is well known that explosives have been necessitated in modern wars as weapons of cutting edge technology, while on the other hand, they have also been used for destruction in land cultivation on a commercial basis. The principle of the explosion and the relationship between the destructive range and amount of explosives have been kept secret under the control of various governments.
Conventionally, land cultivation has been normally performed on undeveloped wilderness, and has not caused serious problems by merely considering the efficiency of blasting. Such blasting may be performed without paying attention to the avoidance of accidents associated with blasting, such as damage by flying rocks, thanks to the tolerance of nature.
However, in recent years, when performing blasting for construction in a small well-developed area, for example in such a country as Japan, or in an area close to human residences, it is of urgent importance to direct blasting, with dangerous explosives which may destroy anything, as technology clearly distinguishing safety and danger, by means of human wisdom, as was done with the "quest of fire" in early human history.
For assuring security which avoids flying rock accidents, importance is given to reducing the amount of explosive. However, when the amount of explosive is reduced excessively, the efficiency of blasting is inherently lowered to an unacceptable degree. Accordingly, it is desired to use the maximum amount of explosive in a range where flying rock will not be caused on the free surface, thus achieving both the security and efficiency of blasting operations.
Under such circumstances, as a method for setting blasting in consideration of both security and efficiency, Hauser's equation has been used. Hauser's equation is directed to a concentrated charge at a single point, and establishes the following equation for achieving both security and efficiency: EQU L=cW.sup.3 (20)
wherein c is a blasting coefficient in the range of 0.25 to 0.45 and W is the least resistant length between the explosive and the free surface of the earth.
Studying Hauser's equation, assuming that the breaking radius D on the free surface is equal to the least resistant length W (i.e., when W=D), the volume of the rock to be broken by the explosive is in a reversed cone-shaped configuration, from a volume of cone, the volume V of the rock to be broken into the reversed cone-shaped configuration is expressed by: EQU V=W.sup.3
Accordingly, the foregoing equation (20) can be modified to: EQU L=cV (20a)
The relational expression L=c.times.V indicates that, in order to make the value of L within the safe range, the charge amount L should be a value within a blasting coefficient range of c=0.25 to 0.45 of the fracture volume V of the rock to be fractured at that charge amount.
In blasting operations using a bar-like charge, in practice, a modified Hauser's equation L=cW.sup.3 is employed. Namely, by replacing W.sup.3 with DWH, Hauser's equation can be rewritten as: EQU L=cDWH (20b)
wherein
c: blasting coefficient; PA1 D: fracture radius in the free surface; PA1 W: line of least resistance; and PA1 H: is a charge hole length. PA1 deriving, on the other hand, on the basis of the modified equation L=cDWH (20b) of Hauser's conventional equation L=cW.sup.3, the safety charge amount L as: EQU L=cW.sup.2 H (20c) PA1 deriving a fundamental equation therefrom, since both members of the above relational expressions are equal: ##EQU5## PA1 and then deriving a fundamental equation since both members of the above relational expressions are equal: ##EQU7## PA1 G1: a free surfase of the earth PA1 .alpha..ltoreq.90.degree.: a blast hole angle relating to the free surface G1 PA1 M: a blast hole length PA1 P: a filler length in the blast hole PA1 N=M-P: a charge length PA1 L: a charge amount PA1 A: charge specific gravity PA1 c: blasting coefficient PA1 D: a fracture radious or interval length PA1 V: a fracture rock volume PA1 W: the line of least resistance between the free surface G1 and the head of the charge length; PA1 deriving a fracture rock volume V to be blasted: EQU V=P.sup.2 M sin.sup.3 .alpha. (1) PA1 deriving a charge amount L from an equation for deriving the volume of a cylinder: ##EQU8## deriving a fundamental equation for a blasting coefficient c which indicates the ratio of (1) to (2): ##EQU9## deriving a filler length P by converting equation (3) to the quadratic equation of the filler length P: ##EQU10## then substituting P.sup.2 obtained by squaring both members into equation (1) to derive the fracture rock volume V: ##EQU11## where the blasting coefficient c in the equation (5) should be within the range of: PA1 c=0.0002-0.0005. PA1 c=0.0002-0.0005.
However, in practical blasting operations, the bar-like charge system is used to charge an explosive within a pit or hole having a certain length H and diameter d. Therefore, the explosive is present as a solid having a certain length (charge length N=H-W) and diameter d, wherein W is the line of least resistance.
Accordingly, when a charge amount L required for blasting using the bar-like charging is derived employing the Hauser's equation, a value far different from the practical amount may be derived to cause significant danger. For example, when blasting of a rock is to be performed employing dynamite stick having a diameter of explosive of 25 mm charged in a hole diameter d=25 mm, the charge amount L derived by Hauser's equation becomes : EQU L=cW.sup.3 =0.25.times.2.sup.3 =2 (kg)
assuming the blasting coefficient c=0.25 and the line of least resistance W=2 m. This charge amount corresponds to a twenty sticks of dynamite having explosive diameter of 25 mm, explosive length of 165 mm, and weight of 100 g. When such dynamite is charged in the 2 m of charge hole, the hole will be filled with 12.5 sticks of dynamite. Thus, the remaining 7.5 charges of dynamite cannot be placed in the charge hole. Therefore, in order to maintain the calculated charge amount, the diameter of the charging hole should be increased to 80 to 100, or more. However, the hole diameter d cannot be derived by using Hauser's equation.
In this respect, charge hole diameter d is typically empirically thought to be at 1/45 of the line of least resistance W (see R. Gusteferson: "New Blasting Technology", Morikita Shuppan K.K., Apr. 10, 1981, pp. 60). Also, the Japan Industrial Explosive Association utilizes similar standards but widens the allowable range and provides a guideline, "In case of typical blasting, the line of least resistance is within a range of from 30 to 60 times the charge hole diameter". In other words, "the charge hole diameter d is from 1/30 to 1/60 of the line of least resistance W" (see Ground Emission Division of Ministry of International Trade and Industry of Japan, "Explosive Safety Text Series 17", January, 1991, pp 24). In a concrete example of this relationship, when a charge hole diameter d is set at 3 cm, the line of least resistance W can be within a range of 90 to 180 cm. Such range is too wide in view of a critical line of least resistance length, and could possibly cause the occurrence of an accident to human beings, and thus is dangerous.
The inventor of the present invention thinks as follows; the reason is that the line of least resistance W in the blasting operation is a value representative of the shortest distance between the upper end of the explosive and the free surface of the earth. When the value of the line of least resistance W is too short, an accident due to flying rocks may be caused. On the other hand, when the value of the line of least resistance W is too long, fracturing at the surface of the earth may become insufficient and lower the efficiency of operation. Therefore, as can be appreciated from the foregoing, the line of least resistance W is believed to be quite an important factor in determining safety and efficiency in blasting operations.
However, the fact that ambiguous relationships between the hole diameter d and line of least resistance W can be set within a wide allowable range should be pointed out in view of both safety and efficiency.
The number of accidents by blasts during construction work in Japan from 1979 to 1989 totaled 261, in which accidents by flying rock accounted for 160 cases (61.3%). This shows that a need to establish a method to set bar-like charges that enable safe and efficient blasting operations.
In order to solve the above-mentioned problems, the inventor has developed a method for determining relational parameters, comprising the steps of, as indicated in Japanese Patent No. 2662691, deriving a charge amount L for a bar-like charge at the charge hole angle .alpha.=90.degree. from the following, formula used to determine the volume of a cylinder: ##EQU4## where d is the blast hole diameter; H is the blast hole length; W is the line of least resistance; N=H-W is the charge length; c is the blasting coefficient; and A is the specific gravity of the explosive;
The inventor has also developed a method for determining the relational parameters, comprising the steps of, as indicated in U.S. Pat. No. 5,650,588 corresponding to Japanese Patent Laid-Open No. 9-113200, deriving a charge amount L for bar-like charges not only at the charge hole angle .alpha.=90.degree. but also in case of .alpha.&lt;90.degree. based on the equation for determining the volume of a cylinder: ##EQU6## where M is the blast hole length; P is the filler length; deriving, on the other hand, from a modified Hauser's equation of the conventional L=cW.sup.3, the charge amount L as: EQU L=cP.sup.2 M sin.sup.3 .alpha. (20d)